Introduction: Arduino Oscilloscope

Picture of Arduino Oscilloscope

A very basic and easy to make arduino PC oscilloscope.

Features:

  • 50K samples/second
    (actually it can go up to 110K but the signal will become noisy)
  • Auto trigger
  • Frequency counter
  • Reasonably accurate voltage readings (depending on the accuracy of the resistors used for the voltage dividers)
  • Optional: selectable voltage range: 5V, 6.6V, 10V, 20V

You'll need:

      • An Arduino Leonardo or Arduino Micro
      • 2 crocodile clamps
      • a 0.1µF capacitor (optional)
      • a 5.1V zener diode (optional)
      • a pc with Processing

      For the voltage dividers (optional, if you want to measure than 5V or want selectable range):

      • 2 two-pole dual throw switches
      • two 3K resistors
      • two 1.5K resistors
      • one 1K resistor
      • a small perfboard or breadboard


      If you only need to measure op to 5V, you can skip the voltage dividers and connect the probes directly to GND and A1. You'll have to modify the code a bit:

      In the arduino code, replace:

      ADMUX =  B00000000;         // select external reference and port 5 (A0)

      with:

      ADMUX =  B01000000;         // select internal reference (Vcc - 5V) and port 5 (A0)

      In the processing code, replace:

      // read switch position & set voltage range
       boolean switch1=((buffer[writeIndex*2]&(byte)8)==8);                                                 
       boolean switch2=((buffer[writeIndex*2]&(byte)4)==4);
       if (!switch1&&!switch2) voltageRange=20;
       if (!switch1&&switch2) voltageRange=10;
       if (switch1&&!switch2) voltageRange=6.64;
       if (switch1&&switch2) voltageRange=5;

      with:

      voltageRange=5;

      Step 1: Adding Voltage Dividers

      Picture of Adding Voltage Dividers

      The circuit show above consists of:


      On the left: a 1:4 voltage divider between the probe and A1

      This will bring the voltage down to 1/4 of the input voltage. The analog pins can handle 5V, so this will allow for voltages up to 20V.

      Note that there are 2 input channels in the picture of the breadboard. Adding an extra channel slowed down the sampling rate dramatically (because continuous mode can't be enabled on the ADC), so I decided to leave it out in the final code.

      On the right: a switched voltage divider between 5V and the Analog Reference (AREF) pin
      You can use the switches to set the measuring range: 5V, 6.64V, 10V of 20V

      How this works:

      If configured to 'external reference', the ADC compares the voltage of the analog inputs with AREF, instead of 5V.
      Here's an example: suppose the probe is measuring 5V. The voltage on the A1 will be 5V/4 = 1.25V

      • If both switches are off, the voltage on the AREF pin is 5V.
        The ADC will read 1.25/5 = 25%
      • If switch 1 is off and switch 2 is on, the voltage on AREF is 2.5V
        The ADC will read 1.25/2.5 = 50%
      • If switch 1 is on and switch 2 is off, the voltage on AREF is 1.66V
        The ADC will read 1.25/1.66 = 75%
      • If both switches are on, the voltage on AREF is 1.25V
        The ADC will read 1.25/1.25 = 100%

      The second pole of each switch is connected to a digital input. We can read this pin to automatically adjust the voltage scale.

      A capacitor between the probe and ground
      Might not be necessary, but for some reason some pc's measure a lot of noise without it. The capacitor will solve that, but may slightly affect the signal when measuring high frequencies.

      A zener between A0 and ground
      To protect the arduino a little from overvoltage or reverse voltage (thanks, tttapa, for the tip!)

      Be careful:

      • If the analog reference is set to internal (default) while you are supplying voltage to the AREF pin, the arduino could get damaged. I did that, and it didn't damage mine, but better be safe and upload the proper code before connecting AREF.
      • the analog inputs can't handle negative voltages.
      • Don't exceed 5V on the arduino pins. It's probably a good idea to test the circuit with a voltage below 5V, so

        you don't damage the arduino in case the voltage divider on A1 was wired incorrectly.

      The arduino code was based on this excellent article:

      http://meettechniek.info/embedded/arduino-analog.html

      Good luck!
      Bram

      Step 2:

      Comments

      NB17 (author)2017-11-12

      Is the code same for Leonardo or are there some changes? And the D3 and D4 pins are pins no. 1/TX and no. 4 (as labeled on Leonardo), correct me if I'm wrong.

      please reply thanks.

      .

      Ahmed RazaS (author)2017-09-28

      Excellent article.It's very helpful.

      I'd like to know if this will work with Arduino Uno and if it will, are there any changes that need to be made? Also, what's the step 2? It doesn't show anything.

      Which program has been used to display the output?

      BramMylemans (author)Ahmed RazaS2017-10-05

      Hello Ahmed,
      Thanks! The UNO uses the serial port for communication over USB. This means less bandwidth than the micro, which uses native USB. It will work, but you probably won't get near 50k samples/sec.
      To display the output you can use the processing app (the download link is in the instructable).

      Best regards,
      Bram

      Ahmed RazaS (author)BramMylemans2017-10-06

      Thanks for the reply.

      I've bought all the required + optional components that you listed out. I'm a bit confused on how to use the DPDT switches. In the required list, it says that only two of such switches are required. But in the circuit diagram, there are four switches used. What will these switches be used for though?

      Another question is how could we produce a particular wave and change the frequency, type of wave, etc? Is all of this included in the application?

      We're making the Oscilloscope as our university mini project. A quick reply will be very appreciated. Thanks, again!

      BramMylemans (author)Ahmed RazaS2017-10-06

      Hello Ahmed,

      SW1a and SW2b on the schematic are 2 poles of the same physical switch, switched simultaneously (one to attenuate the signal, and the other to let the arduino know that the signal is attenuated, so it can adjust the scale).

      This project will not generate wave forms. You could use low voltage AC or audio for a demonstration. If you want to control frequency, shape and amplitude, you'll need (to build) an oscillator.

      Good luck!
      Bram

      Ahmed RazaS (author)BramMylemans2017-10-06

      I see.

      Will I be able to show wave forms using this project if I connect it to a Function generator? Or does this work on its own?

      What are the functions that this oscilloscope will be able to perform?

      maryclair (author)2017-10-02

      Great project. Thank you for help. I am experiencing some difficulties with the graph on the processing program. the graph is not showing the accurate voltage on the screen. For example, if i put in 2V, it only shows a couple of milivolts on the display/graph shown on the processing program. PLEASE HELP!!

      BramMylemans (author)maryclair2017-10-05

      Hi Maryclair,
      What type of arduino did you use? If you have a voltmeter, try measuring between Aref and GND pin and between A0 and GND, to check if the voltage dividers and switches are set up correctly.

      maryclair (author)BramMylemans2017-10-05

      I am an Arduino Micro and I did measure the Aref and GND pin and it was correct. I even went ahead to use an oscilloscope to see and both the graph and reading I saw was fine. it was just not coming out right in the processing display.

      SamirTafesh made it! (author)2016-03-06

      Nice Instructables, i reproduce it and it is working as expected, good work and thank you, i learned a lot

      maryclair (author)SamirTafesh2017-10-02

      I am experiencing some difficulties with the graph on the processing program. the graph is not showing the accurate voltage on the screen. For example, if i put in 2V, it only shows a couple of milivolts on the display/graph shown on the processing program. PLEASE HELP!!

      emallon (author)2016-08-30

      Nice work with the scaling/ranging. I've recently started noodling around with the serial plotter tool in place of processing, and it was relatively easy to emulate a triggered sweep function with a simple threshold triggered loop:

      https://edwardmallon.wordpress.com/2016/08/15/usin...

      maryclair (author)emallon2017-10-02

      I am experiencing some difficulties with the graph on the processing program. the graph is not showing the accurate voltage on the screen. For example, if i put in 2V, it only shows a couple of milivolts on the display/graph shown on the processing program. PLEASE HELP!!

      sommarjobbarna17 (author)2017-07-12

      hello bram! first off, very nice project, I get some really good measurements even though i use the UNO and not the arduino specified in the instructable. but i do have one slight issue, i get some strange noise. between the noise the measures are accurate but pretty much unreadable. i read somewhere in the comments that this could happen if you used the UNO but i couldn't find a solution for it. do you have any suggestions on what i can do to cancel out the noise? i use the scopeP3 code and the 5v read only setup, so nothing extra but the arduino itself.

      thanks in advance

      Hello,
      (Sorry for the late reply, It's been a while since I checked here.)
      It might have to do with power supply noise. Have you tried disconnecting your laptop and running it of the battery?

      Kind regards,
      Bram

      Hello, please what do i do with the pde file (ScopeP3 and scopeP2). I cannot get the oscilloscope screen to show. I was using just the scope.ino code. please help!!!

      BramMylemans (author)maryclair2017-09-21

      Hi,
      You should open it in Processing 2 (scopep2.pde) or Processing 3 (scopep3.pde). You can download processing for free at processing.org. Good luck.

      Best regards,
      Bram

      MauroB28 (author)2017-06-04

      Could I use this project with Arduino Nano ?, which would have to move

      MegaDAS (author)2016-12-23

      cool stuff

      desmondtheredx (author)2016-11-18

      exactly 44 thousandth view 44000

      GaneshG26 (author)2016-03-20

      Hello,

      I do not own a Micro or Leonardo, but I own an Uno. Will this instructable still work with the Uno?

      Thanks.

      BramMylemans (author)GaneshG262016-03-20

      Hello Ganesh,
      It will work, but the sample rate would be limited by the serial speed.
      (You'll need about 800.000 bps for 50K samples/sec. I don't know how fast the uno's serial can go.)

      Regards,
      Bram

      it can go upto 115200baud or bps

      Someone on this thread claims his UNO goes up to 2Mbps.
      Perhaps the 115200baud is a limitation of arduino IDE's serial monitor?

      see, the arduino CAN do 921600 baud, just the ide only goes to 115200

      >Perhaps the 115200baud is a limitation of arduino IDE's serial monitor?

      it indeed is. HyperTerminal can go upto 921600 baud. But anything above 115200 baud is lossy and subject to line interference so it is hardly ever used.

      nsoclo (author)BramMylemans2016-05-25

      Mr. Bram, how you can assumption 50k sps need 800.000 bps? can you explain to me? thx

      BramMylemans (author)nsoclo2016-05-25

      Hello Nsoclo,

      50,000 samples/sec * 16 bits/sample = 800,000 bits per second.

      Regards,
      Bram

      nsoclo (author)BramMylemans2016-05-31

      16 bits/sample ? in specification, Arduino ADC is 10 bit. why it can 16 bits/sample?

      tanks you very much Sir !

      BramMylemans (author)nsoclo2016-05-31

      You're right, one sample is 10 bits, plus two bits for the switches, but it is sent as 2 bytes for simplicity (and because it doesn't matter on an arduino micro, where the ADC rate is the limiting factor).

      nsoclo (author)BramMylemans2016-05-31

      thanks your information Sir, its helpfull.

      Regards,

      Narto

      R Jordan Kreindler (author)2016-07-11

      An interesting topic. Nice job!

      nevillekong1 (author)2016-03-22

      I like your oscilloscope! But I think it's better to show the result with a LCD ;)

      PumidolL (author)2016-03-07

      Hi,

      I get an error on this line

      serial = new Serial(this, Serial.list()[keyCode-112], serialBaudRate);

      errpr: ArrayIndexOutOfboundsException:-122

      Im on OSX 10.11.1 thanks!

      BramMylemans (author)PumidolL2016-03-07

      Hell Pumidoil,
      I can't test on Mac, but try pressing Fn together with the function key to select the serial port. Maybe Mac defaults to Fn lock.
      If that doesn't work, replace (in processing):

      serial = new Serial(this, Serial.list()[keyCode-112], serialBaudRate);

      with:

      serial = new Serial(this, COM3, serialBaudRate);
      //(replace COM3 with the right port)

      Let me know if it still doesn't work.

      PumidolL (author)BramMylemans2016-03-07

      Hi,

      Thanks for fast reply! You just gave me the idea. It's the Fn button that freezes the program.

      I used onscreen keyboard to select COM port. Now it works flawlessly.

      brajomobil (author)2016-03-02

      Can you please explan how did you get 50k samples per sec?
      When I log raw data from serial port I can get max 12k samples per sec.
      Thank you In advance.

      BramMylemans (author)brajomobil2016-03-02

      Hi Brajamobil,

      Are you using analogRead? If so, have a look at: http://meettechniek.info/embedded/arduino-analog.h..., and the atmega datasheet.

      The frequency can be increased by:
      - lowering the prescaler of the ADC, so it will run at a higher frequency.
      - setting the ADC to continuous mode, with an interrupt to read the data into an array.
      - sending multiple samples at a time (because each serial.write command has some overhead)

      brajomobil (author)BramMylemans2016-03-02

      Hi Bram,

      I'm using your "scope.ino". In your code I don't see 50K samples going over
      serial port. I have installed serial logger to see If I am missing something.
      I am not questioning ADC sampling at 50K, just transferring that data over serial line. Serial baud is not enough.

      BramMylemans (author)brajomobil2016-03-02

      Sorry, I misunderstood.
      What exactly does the serial logger count? 12K bytes/sec?
      Have you tried the processing sketch?

      brajomobil (author)BramMylemans2016-03-03

      I tried your processing sketch. Refresh rate is not high because serial line is slow by design. You can't trasfer 50K samples over it. Search google for explanation of baud. After that please explain how did you manage to transfer that amount of data over it. If you can't then please correct your instructable.

      BramMylemans (author)brajomobil2016-03-03

      Hey Brajamobil,

      Apparently the Micro and Leonardo don't use the UART for USB communications. They ignore the baudrate set in serial.begin(xxx), and allow for much faster speeds (up to 12Mbit/s).
      Thanks for pointing this out. I've updated the instructable.

      Akshay Jha (author)2016-02-29

      Hii first of all thanks for this instructables . I am facing problems in measuring voltage more than 5volts it losts its accuracy below 5 volt it works fine but when I set switches on like 20v confriguation and it is also showing 20 volt on processing output but after this I applied 11v on probes it shows around 19 volts

      BramMylemans (author)Akshay Jha2016-03-01

      Hi Akshay,

      If you have a voltmeter you could try measuring:
      - between A0 and GND: should be 1/4th of the voltage at the probe
      - between AREF and GND: depending on the switches, this should be 5V (20V scale), 2.5V (10V scale), 1.66V (6.66V scale) or 1.25V (5V scale)

      If all these are correct, perhaps pins D3 or D4 are connected to the wrong poles of the switches, selecting the wrong voltage scale. You can invert pins D3 and/or D4 in processing:
      boolean switch1=!((buffer[writeIndex*2]&(byte)8)==8);
      boolean switch2=!((buffer[writeIndex*2]&(byte)4)==4);

      Good luck! Let me know if it still doesn't work.

      Akshay Jha (author)BramMylemans2016-03-01

      Thanks for the reply but unfortunately it doesn't work
      1. I've check voltage between A0 & Gnd it is giving exactly 1/4th of voltage
      2. I've also checked votage at Aref pin it also as you've mentioned
      3. At last I ve modify code according to you but it give me wrong values
      But it is working great below 10 volts but when I set switches to 20 volt mode it gives unwanted noise which was not present in any other confriguation

      BramMylemans (author)Akshay Jha2016-03-01

      Hi Akshay,
      Strange. The only thing I can think of is that AREF is left floating when both switches are on. Have you tried connecting AREF directly to the arduino's 5V pin? (this should give you the 20V range)

      Akshay Jha (author)2016-03-01

      You can see this unwanted noise but must tell you that lower than 10v it works very well

      Dimitrisblamis (author)2016-02-10

      What is the maximun frequency it can measure?

      In theory, half the sampling rate, about 25KHz. But you won't be able to distinguish the shape of the wafevorm anymore.

      magkopian (author)BramMylemans2016-03-01

      With only two samples you can't represent any signal accurately unless it's a perfect square wave. In practice you need at least 10 samples of each period of the signal in order draw it accurately enough on the screen (by joining the dots), which means the maximum frequency is around 5Khz. Still pretty good for many low frequency applications though.

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